Process of producing photographic silver halide emulsions utilizing sulfonated polyphenylene oxide



United States Patent W 3,137,576 PROCESS OF PRQDUCWG PHOTOGRAPHIC SILVER HALIDE EMULSIQNS UTILIZING SULFQNATED POLYPHENYLENE OXIDE Wolfgangv Himmelmann, Cologne-Stammheim, Helmut Miider, Leverkusen, and Rolf Fred Posse, Cologne- Flittard, Germany, assignors to Agfa Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany -No Drawing. Filed (let. 16, 1962, Ser. No. 231,094 Claims priority, application Germany Oct. 25, 1961 6 Claims. (Cl. %-94) The invention relates to a silver halide emulsion and a process for their production.

-According to the conventional method, .the silver halide is precipitated in gelatine solution and the resulting emulsion thereafter solidified by cooling and the gel is cut into pieces and freed from soluble salts by washing with cold water. On account of the diffusion velocity of the salts, this process necessitates certain rinsing periods. Depending on the nature of the gelatine, the volume of the gel increases to a large or small degree and frequently an undesired lowering of viscosity occurs. This must often be compensated for by adding gelatine during the subsequent melting (ripening or casting). Using this process, it is difficult to vary the ratio between silver halide and gelatine as required.

More modern processes produce emulsions with a high silver content. In such a process, the emulsions are coagulated by adding a precipitant to remove the excess salts, separated from the supernatant aqueous. solution containing the salts in dissolved form, washed with water and, after adding more gelatine solution, often also redispersed. by adjusting the pH to a predetermined value. It is possible in this way to obviate the rinsing operation which occupies a considerable time. In addition, the emulsion character can be varied greatly and improvements in the photographic properties can be obtained. It is to be'remembered that with the conventional method, the gelatine solution must have a minimum concentration of about 23% in order to achieve the gelling of the gelatine. The increasing importance of this flocculation process is illustrated by the large selection of variants of the process which have become known in recent times. They 'dilfer from one anotherv more especially by the nature of the precipitant.

The oldest method of flocculating gelatino-silver halide emulsions is salt flocculation. An excess of, for example, sodium sulphate is added to the emulsions and the gelatine flocculates out with the silver halide. The disadvantage ofthis method lies in the great excess of salt which is necessary for a complete flocculation. In addition, such precipitates cannot be washed out with water, since they are easily dissolved again. After the washing process, the emulsions still show a certain conductivity, which is attributed to a high residual content of salts.

Furthermore, organic liquidswhich are miscible with water and in which the gelatine is insoluble have been proposed for flocculating the emulsions. The disadvantage of this method lies in the fact that there is a high consumption of organic solvents and that various salts which'are insoluble in the solvent mixture are also precipitated. It is not possible for the coagulates to be washed out with water, so that it is necessary to use a solvent mixture. Methods which are said to improve the washing-out ability of these methods have alsobeen proposed, but they have the same disadvantages.

Another method of flocculating emulsions consists in chemically converting the gelatine. For example, gelatine can be reacted with phthalic acid. anhydride and added to the batch gelatine.

A 3,137,576 Patented June 16, 1964 can be precipitated in aqueous solution at pH 3. How ever, the production of the gelatine derivatives often leads to difi'iculties as high pH values (in the region of 10) must be used during the reaction. As a result, some of the gelatine is decomposed. Furthermore, derivatives of this type do not permit the production of highly sensitive emulsions. When using these flocculating agents, the photographic properties of the emulsion are so greatly influenced that these precipitation methods cannot be used on existing and tested emulsion recipes, sincethey influence the composition of the ripening and inhibiting elements to a large extent. For these reasons, a complete redevelopment of the photographic emulsion concerned is usually necessary. This disadvantage has hitherto prevented the practical use of this process.

There have also been described as flocculating agent, compounds which either form complexes with the gelatine or are even insoluble'in Water at certain pH values. With the precipitation thereof, the gelatine is also entrained. For example, alkyl-sulphonic acids containing a high number of carbon atoms (C C have been proposed. With the gelatine they form adducts which The gelatine derivatives are insoluble at pH 2-3. A disadvantage in this case is the large amount of the respective sulphonic acids (20-30%) which have'to be added, the casting difliculties which are a consequence thereof and the relatively low pH value of the precipitation. It is known from practice in the production of emulsions that the sensitivity of ahighly sensitiveemulsion decreases as the pH value becomes too acid 4).

High-molecular acid-insoluble compounds with carboxyl groups have also been proposed as flocculants. In this case, the relatively low flocculation pH value and the modification of the physical properties of the gelatine, for example, the water permeability, the high swelling, the modified adhesion and the impaired redispersability, constitute disadvantages. Benzaldehyde sulphonic acid acetals of polyvinyl alcohol have also been described as flocculants, but these have the disadvantage that the coagulates of the acetalsulphonic acids and gelatine are only formed at pH values below 3. Another process which i's known is the precipitation of emulsions of co polymerswith vinyl pyridine and unsaturated carboxylic acids, but this process has the disadvantage that relatively large quantities of copolymer are required for precipitating the emulsions, since the pyridine radical becomes ionised in acid solution, whereby the solubility of the coagulate in acid solution increases. Furthermore, the photographic properties of the emulsion are modified in an uncontrollable manner by the pyridine radicals. Finally, it is known to use copolymers of styrene-sulphonic acids for flocculating gelatine, but these have similar disadvantages to those of the aforementioned polymers.

It has now been found that salts of water soluble high molecular weightpolyphenylene oxides containing sulphonic acid groups precipitate silver halide emulsion at pH values of 3.5-6. The subtances can be used according to the invention for precipitating'all types of such emulsions. However, they are especially'suitable for emulsions having a lowgelatine'content and a particularly high 'silver'halide content, such emulsions are characterised by a silver halide gelatine proposition of at least 1 g. silver halide per 1.5 g. of dried gelatine. A precipitation from highly diluted aqueous solution also occurs without it being necessary to addsalts or organic liquids. The gelatine is'completely precipitated by the substance according to the invention. The photographic properties of the silver halide emulsions-or the gelatine compositions are not changed thereby. By-means of the process according to the invention, it is possible for any desired silver halide emulsion to be produced'subst'antially more easily than was possible with the hitherto known processes. The compounds according to the invention are particularly advantageous over prior art because they are capable of almost completely precipitating the gelatine respectively the silver halide. Thus a loss of silver salts is avoided.

Especially suitable for the precipitation of the silver halide emulsions are polyphenylene oxides of the general formula:

t a t R3 1% r A. I i: 1L. 1 14 A I ia 11 in which R to R represent hydrogen atoms or an alkyl radical containing 1 to 3 carbon atoms; A represents a 'hydrogen atom or a --SO Me-group, but 1 to 3 and preferably 2 neutralised sulphonic acid groups must be present for each formula unit (i.e. for every three phenylene oxide radical); Me represents any desired alkali metal such as sodium or potassium, alkaline earth metal by magnesium or calcium or ammonium cation, for example, ammonium or alkyl ammonium cations and n represents an integer between 3 and 100.

The eitect produced by this process was all the more surprising, as salts of polyphenylene oxide sulphonic acids are readily soluble in water and the corresponding sulphonic acids cannot be precipitated by acidification of their solutions or salt solutions. On account of the numerous oxygen bridges, it had to be assumed that large quantities of polyphenylene oxide sulphonic acid are required for precipitating the gelatine. The advantage of this compound is that for completely precipitating gelatine at a pH value of 3.5-6, it is only necessary to use a relatively small quantity, namely 8 to 20% and advantageously 10l2% of the weight of gelatine, so that the fiocculate can be washed out extremely satisfactorily and so that the fiocculate can be redispersed very quickly and without residue by adjusting the pH value to about 7 and by gently heating the mixture to 35-45 C.

Another discovery which was particularly surprising to the persons skilled in the art was that the compounds according to the invention do not have any deleterious eli ect on the photographic properties of the silver halide emulsion. This was not to be expected, since, for example, aliphatic polyethylene oxides are known to have strong influence on the sensitivity of photographic emulsions. In the case of the polyphenylene oxides used according to the invention, the sensitivity and the gradation of the emulsion are not changed. The emulsion is only improved by suppressing the fogging, probably due to the possibility of being able to redisperse the coagulate quicker.

The production can be supplied by this method while maintaining the tested emulsion recipes. The procedure adopted is that the silver halide is precipitated in the batch gelatine. 23-20% of a water-soluble salt of polyphenylene oxide sulphonic acid, calculated on the quantity of gelatine used is added to this dispersion. The pH value is then adjusted to between-3.5 and 6. The emulsion coagulates in the form of fine flakes, the size of' which can be varied within certain limits by adjusting to a predetermined temperature. Large flakes and coherent coagulates are obtained when working at relatively high temperatures.

After the settlement of the emulsion, the supernatant liquid is removed by decantation and the precipitate is washed several times with cold water; The residue can be redispersed extremely easily and quickly with water at a temperature below 45 C. by adding alkali until a pH value of 78 is reached. The required quantity of gelatine is added and the emulsion is ripened. The conventional additives, such as sensitisers, stabilisers and hardeners, can also be added.

' sas /3.57s

According to a modified form of the process, the pH is adjusted to a value of 3.54 and the substance is cooled to 12' C. above the solidification point of the gelatine. If an aqueous solution of a salt of the polyphenyl sulphonic acid is added under these conditions, the emulsion precipitates in finely divided form and can be extracted by suction filtering. The redispersion then proceeds even more quickly.

The method referred to can also be used in order to produce new emulsions with extremely high silver halide content.

Furthermore, it is possible to add other layer-forming natural or synthetic polymers after the redispersion. T hus, highly sensitive silver halide layers based on synthetic plastics, for example, polyvinyl alcohol, hydroxyethylcellulose or cellulose esters, can be produced. These were otherwise only obtained with photographically active .gelatine.

Larger quantities of polyphenylene oxide sulphonic acids can be added to the emulsions without any photographic dei'ects being caused. In addition, such emulsions have a higher conductivity and do not have such a strong tendency to electrostatic charging. The mechanical strenth of the rinsed layers is good.

The sulphonic acids of the polyphenylene oxides have, as yet, not been described in the literature. Polyphenylene oxides are known and they are prepared from the corresponding phenols. Aqueous solutions of pbromophenols are condensed with sodium hydroxide solution, sodium bromide being split off (JACS 82 (1960), No. 14,

page 3632; Journal Polym. Science, volJXLIX (1961), page 267-275), or the silver salt of the alkylated bromophenol is initially used and thereafter condensed, silver bromide being split off.

According to another method, the corresponding dialkyl phenols are condensed by oxidation, the phenol being dis.- solved in nitrobenzene and oxygen being introduced in the presence of cuprous salts and pyridine (JACS 81 (1959), 5

PRODUCTION OF POLYPHENYLENE OXIDE SULPHONIC ACID A solution of 65 cc. of ethylene chloride and 13 g. of dichloro-diethyl ether is stirred at 20 C. 2.1 cc. of sulphur trioxide, stabilised with HCl, are added to the mixture. A solution of 5 g. of polyphenylene oxide in 65 cc. of ethylene chloride is slowly added dropwise at 20 C. The mixture is stirred for another 2 hours, it being possible for the temperature to rise to room temperature. The mixture is concentrated to 30 cc. by evaporation and the sulphonic acid is thereafter precipitated with ethylene chloride, suction-filtered and dried (yield: 8 g.). It is thereafter neutralised in a little water with sodium hydroxide solution 1-! group content: 15.7%

SULPHONATION OF THE POLY-2,6-DIMETHYL- 1,4-PHENYLENE OXIDE 6.3 cc. of sulphur trioxide stabilised with HCl is intro- 5 2,2-dichloro-ethyl ether is formed. After cooling the mixture to 20 C., 9 g. of poly-2,6-dimethyl-l,4-.

phenylene oxide (prepared according to (JACS 81 (19 59), No. 23, page 6335)) in ml. of dichlorethane SULPHONATION OF POLY-2,6-DIETHYL- 1,4-PHENYLENE OXIDE The sulphonatiorY is eifected as above, except that the following quantities are used:

200 ml. dichloroethane 62 g. of 2,2-dichloro-diethyl ether 8 ml. of sulphur trioxide 10 g. of poly-2,6-diethyl-1,4-phenylene oxide in 100 ml. of dichlorethane Yield of sodium salt: 15 g. SO H group content: 21.2%.

Example 1 A photographic emulsion is prepared from the following solutions by mixing at 50 C.:

Solution A- 10 g. of gelatine 64 g. of potassium. bromide 3.6 g. of potassium iodide 500 cc. of water Solution B--- 80 g. of silver nitrate 600 cc. of water 4.5 cc. of a 5% aqueous solution of the sodium salt of a poly-2,6-dir'nethyl-1,4-phenylene oxide sulphonic acid are added to 200 cc. of this emulsion at 45 C. After adjusting the pH value to 3.5-4 with dilute acetic acid or citric acid, a finely flocculated coagulate is formed.

The mixture is cooled to 20 C., the supernatant liquid is poured off and the coagulate is Washed with cold water. The coagulate is thereafter redispersed by adding 24 g. of gelatine in 300 cc. of water at 40 to 50 C., the pH value being adjusted to 7. The emulsion has the same sensitivity as the emulsion prepared in conventional manner and the gradation has also not changed.

Example 2 A photographic emulsion is prepared by mixing the following solutions:

Solution A- 1200 ml. of water 300 g. of silver nitrate 300 ml. of ammonia solution (d.=0.91) Solution B 700 ml. of water 300 g. of potassium bromide 6 g. of potassium iodide 70 g. of gelatine The solution A is added dropwise over a period of 30 minutes at a temperature of 40-45 C. to the solution B while being thoroughly stirred. After cooling to 30 C., 70 cc. of a 10% aqueous solution of the sodium salt of a poly-2,6-diethyl-phenylene oxide sulphonic acid are slowly added While continuing stirring. The emulsion is approximately neutralised by adding 160 cc. of glacial acetic acid and thereafter fiocculated out by further addition of dilute acetic acid until a pH value of 4 is reached. The flocculate is freed from the liquid by decanting and then washed several times in cold water. The pH value is adjusted to 6.6 with dilute sodium hydroxide solution and the flocculate is redispersed by adding 120 g. of gelatine in 1200 cc. of water. The emulsion thus obtained is ripened in the usual manner at 50 C.

canted. off. from the flocculate.

, Example 3 A pho tographicemulsion is prepared from the following solutions:

Solution A- 100 g. of silver nitrate are dissolved in 300 cc. of water and r f 100 cc. of ammonia solution (d.='0.91) "are adde Solution B 100 g. of gelatine,

100 g. of potassium bromide and j 10 cc. of 10% potassium iodide solution are dissolved 600 cc. of water and the mixture is heated to'40 C. The solution Ais introduced dropwise over a: period of 5 minutes into solution B. After stirring :for another 10 minutes, 12. g. of the sodium salt. of poly-2,6-diethylphenylene oxide, sulphonic acid dissolved in 120 cc; of water are added and the mixture is cooled to 35 C. The mixture is approximately neutralised with cc. of 25% sulphuricacid and thereafter the coagulate is obtained by dropwise addition of acetic acid. The most favourable pH rang'eis 3.5-4. The clear solution is de- The flocculate is thereafter washed two or three times with cold water. The flakes are redispersed in 500 cc. of water at 40 C. and dilute sodium hydroxide solution is added toadjust the pH value to 7.2. .A solution of 200 g. of gelatine in 1.5 litres of water is added and the emulsion is ripened for about v.60. minutes at 50 C. By comparison with an emulsion prepared in' the usual way, the'emulsionhereby obtained does not show any change in its photographic properties.

Example 4 An emulsion is prepared by mixing the following solutions at 45 C.:

Solution A 900 cc. of water 15 g. of gelatine g. of KBr Solution B g. of silver nitrate 1000 cc. of Water Solution B is added to solution A and, after cooling the mixture to 35 C., 15 cc. per 1 litre of emulsion of a 10% solution of the sodium salt of an unsubstituted polyphenylene oxide sulphonic acid is added. The pH is adjusted to 4.0 to 4.5, and the emulsion flocculates out. It is thereafter decanted and the precipitate is redispersed by adding 35 g. of gelatine in 500 cc. of water after adjusting the pH to 7 and heating to 40-50 C. after the usual ripening, the emulsion obtained does not differ from an emulsion prepared in the conventional way.

' Example 5 A photographic emulsion is prepared from the following solutions:

Solution A- 100 g. of silver nitrate 550 ml. of water Solution B 45 g. of sodium chloride 1200 ml. of water 12 g. of gelatine Solution A is introduced dropwise into solution B while stirring vigorously and at a temperature of 50 C. After cooling to 35 C., 600' ml. of the emulsion thus prepared is adjusted to a pH value of 4.0-4.3 with 3% sulphuric acid. The emulsion is fiocculated out and separated by decantation from the supernatant liquid by adding 15 ml. of a 5% aqueous solution of the sodium salt of poly-2,6-diethyl-phenylene oxide sulphonic acid. The soluble salts are removed from the flocculate by repeatedly washing with cold water. The fiocculate is thereafter redispersed by adding 35 g. of gelatine in 500 ml. of water. This is then heated to 40-50 C. and the pH value adjusted to 7.

Example 6 3 samples of a silver halide gelatine emulsion are prepared, using for each sample 280 g. of gelatine 1200 g. of silver nitrate 850 g. of potassium bromide l. of Water AgBr content grams The pH value forthe precipitation of 3.5-6 can be adjusted by the addition of mineral acids, such as sulfuric acids or organicacids. Preferred are monoor polybasic aliphatic acids, such as acetic acid and citric'acid. We claim:

1. A process for the production of photographic silver halide emulsions, which comprises coagulating a silver halide dispersion in an aqueous gelatine solution by addin}; to said solution at a pH value of about 7 a water soluble salt of a sulfonated polyphenylene oxide, adjusting the pH value to a value of between about 3.5 and 6 by addition of a water soluble acid selected from the class consisting of mineral acids and organic acids to cause the gelatine to precipitate asa coagulum from the solution; separating the coagulum from the supernatant liquid,

washing said coagulum with water and redispersing it at a pH value of at least 7, said sulfonated polyphenylene oxide having the following general formula:

F A l i A l a A 5 I L A. B2 i k R4 1L Ru 11 wherein R to R represents a member selected from the group consisting of hydrogen and alkyl radicals up to 3 carbon atoms; A represents a member selected from the class consisting of hydrogen and a neutralized sulfonic acid whereby the sulfonie polyphenyl oxide contains 1-3 sulfonic acid groups for each formula unit of three phenylene oxide groupings and n represents an integer between 3 and 100.

2. A process according to claim 1, wherein said. sulfonated polyphenylene oxide has a molecular weight between 1000 and 30,000.

3. A process according to claim 1, wherein said sulfonated polyphenylene oxide is added in concentrations of 820% based on the dry weight of the gelatine.

4. A process according to claim 1, wherein said sulfonated polyphenylene oxide is a sulfonated 2,6-dimethyl polyphenylene oxide.

5. A process according to claim 1, wherein said sulfonated polyphenylene oxide is a sulfonated 2,6-diethyl polyphenylene oxide.

6. A process according to claim 1, which comprises coagulating a silver halide dispersion in an aqueous gelatine solution, which contains per 1.5 g. of dispersed gelatine at least 1 g. of silver halide by adding to said solution said sulfonated polyphenylene oxide.

No references cited. 

1. A PROCESS FOR THE PRODUCTION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS, WHICH COMPRISES COAGULATING A SILVER HALIDE DISPERSION IN AN AQUEOUS GELATINE SOLUTION BY ADDING TO SAID SOLUTION AT A PH VALUE OF ABOUT 7 A WATER SOLUBLE SALT OF A SULFONATED POLYPHENYLENE OXIDE, ADJUSTING THE PH VALUE TO A VALUE OF BETWEEN ABOUT 3.5 AND 6 BY ADDITION OF A WATER SOLUBLE ACID SELECTED FROM THE CLASS CONSISTING OF MINERAL ACIDS AND ORGANIC ACIDS TO CAUSE THE GELATINE TO PERCIPITATE AS A COAGULUM FROM THE SOLUTION, SEPARATING THE COAGULUM FROM THE SUPERNATANT LIQUID, WASHING SAID COAGULUM WITH WATER AND REDISPERSING IT AT A PH VALUE OF AT LEAST 7, SAID SULFONATED POLYPHENYLENE OXIDE HAVING THE FOLLOWING GENERAL FORMULA: 